Benzoxazine compounds have been employed satisfactorily to produce prepregs, laminates, PWB's, moulding compounds, sealants, sinter powders, cast articles, structural composites parts and electrical and electronic components by impregnating operations and infusion processes. Such resins are dimensionally stable and have good electrical and mechanical resistance, low shrinkage, low water absorption, medium to high glass transition temperatures and good retaining properties, in terms of mechanical properties.
Benzoxazine compounds can be produced in several ways. First of all, by using a process based on solvents cf. U.S. Pat. No. 5,152,993 or U.S. Pat. No. 5,266,695. Secondly, as for example described in U.S. Pat. No. 5,543,516, the preparation of benzoxazines is disclosed without using solvents.
The flame resistance, despite the fact that it compares favorably with that of other polymeric resins resistant to high temperatures, such as for instance epoxy resins is still not sufficient for many uses. In order to make benzoxazines flame retardant the addition of bromine, phosphorous, chlorine containing compounds, fillers or the use of special flame retarded backbones in benzoxazines as it is described for example in EP 0458739, EP 356 379, U.S. Pat. No. 5,200,452, U.S. Pat. No. 5,152,939 or in EP 1366053, JP2001220455 is necessary. Very often the offered solutions to make a composition flame retardant is based on inert fillers or halogen containing compounds or other additives which have as a rule one or several drawbacks:                They are not soluble in solvents and hence cause problems in terms of processing.        They show poor oxidative stabilities at elevated temperatures.        Additives are very often responsible for a decrease of the glass transition levels.        Very often poor physical properties of the cured resins are been observed, cf. U.S. Pat. No. 512,939.        Toxic gases of combustion may form in case of fire, especially when halogenated compounds are present.        